NATURE 
[ Oct. 5, 1871 





















a 













experiments that the ratio of diminution of radiant heat 
transmitted to a stationary thermometer by an incan- 
descent circular disc of cast-iron, turning on appropriate 
journals, is directly proportional to the sines of the angles 
formed by the face of the disc and lines drawn to the 
centre of the bulb of the stationary thermometer. It 
was clearly shown that those heat rays only which are 
projected at right angles to the face of the incandescent 
radiator, transmit maximum energy. The important 
bearing of this fact with reference to temperature tran- 
smitted by the heat rays of the photosphere from points 
near the border, is self-evident. The small angle formed 
by the ray ¢g, Fig. 6, and the tangent c f of the sur- 
face of the photosphere at c, explains satisfactorily why 
the radiant heat at a distance of .1, of the radius from 
the sun’s border, is considerably less than at the centre. 
It will be perceived that the angle fc @ diminishes very 
rapidly as the border of the photosphere is approached, 
and that when the extreme point is reached, the radiant 




ab=10000 cd=2?0012 
heat transmitted would be infinitesimal if the irregularity 
ct the supece of the photosphere did not present a series 
of incline anes capable of projecting hez i 
direct line with El. e Benne ee ae 
Laplace, in the famous demonstration by which he 
proves that ‘‘if the sun were stripped of its atmosphere 
it would appear twelve times as luminous” (Mecanique 
céleste, tom iv., pp. 284—288), commits the grave mis- 
take of assuming that all rays emanating from a radiant 
surface possess equal energy. This assumption leads 
him further to the erroneous conclusion that the rays pro- 
jected from the retreating surface of the sun near the 
limb, act as rays from a lens, being crowded together in 
consequence of the obliquity of the radiant surface 
thereby, he supposes, acquiring increased intensity — 
hence the monstrous assertion of the great mathematician 
that, but for the interference of the solar atmosphere 
the luminosity would be eleven times more intense. ; 
The important question whether the solar atmosphere 
possesses any appreciable radiant power, and whether the 
od ‘ 
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